1. Field of the Invention
This invention relates to a pressure sensor for detecting a differential pressure between two spaces as a relative pressure.
2. Description of the Related Art
JP-A-8-236788 discloses a pressure sensor for detecting a relative pressure. The pressure sensor has a substrate having a micro cavity therein and a hole formed from the back surface of the substrate to communicate with the micro cavity. In this constitution, however, it is necessary to use an alignment apparatus for determining the position of the micro cavity from the back surface of the substrate. In addition, when the hole is formed by anisotropic etching, dimensional variation of the etched hole is large. It is therefore difficult to miniaturize the cavity for performing positioning between the hole and the cavity.
To solve these problems, JP-A-5-52691 proposes a pressure sensor, which can detect a differential pressure by using two pressure sensitive elements to thereby determine a relative pressure. Specifically, two pressure sensitive diaphragm chips are provided on a glass base having two conduction pipes therein, and are air-tightly covered with a sealing case, thereby forming one pressure reference chamber.
In this pressure sensor, however, the sensor constitution is complicated as a whole. Further, it is necessary to perform steps for bonding the diaphragm chips to the glass base, and for forming the pressure reference chamber by the separate sealing case, in addition to steps for manufacturing the diaphragm chips from a wafer. This results in increased cost for manufacturing the pressure sensor.
The present invention has been made in view of the above problems. An object of the present invention is to provide a pressure sensor capable of detecting a relative pressure with a simple and low-cost structure.
According to the present invention, a pressure sensor has first and second sensor elements each having a semiconductor substrate having a pressure reference chamber, a diaphragm formed as a wall defining the pressure reference chamber, and a conversion member for converting deformation of the diaphragm into an electric signal. The first and second sensor elements are respectively disposed in first and second pressure spaces, which are separated from each other to have first and second pressures. A differential pressure between the first and second pressures is detected by a difference between outputs from the first and second sensor elements.
Because the pressure sensor of the present invention is composed of the two sensor elements each having the pressure reference chamber, the pressure sensor is simple in structure and manufactured readily at low cost.
Preferably, a signal processing element for constituting a signal processing circuit for processing the electric signal is provided.in one of the first and second sensor elements. Accordingly, the pressure sensor can have a more simplified structure.